1. Field of Invention
The present invention relates to the document sensor of a sheet feed scanner. More particularly, the present invention relates to a document sensor that can be fabricated at a considerably reduced cost.
2. Description of Related Art
Due to rapid progress in the electronic manufacturing industry, high performance computing systems are produced en-mass. With the proliferation of electronic products in the market, many of them are used in our daily life. In recent years, processing speed and storage capacity of computer products has also increased at a tremendous pace leading to higher performance for many types of graphic processors. Consequently, different types of image processing products such as optical scanners and digital cameras are constructed.
According to the document scanning method, optical scanners can be classified as belonging to: a packet scanner, a sheet feed scanner, a drum scanner or a flatbed scanner. As an example, a sheet feed scanner can have an optical resolution in excess of 600 dpi and almost all of them have a scanning structure that employs contact image sensors (CIS). In fact, the sheet feed scanner occupies such a small volume that they are routinely carried along with a notebook computer.
In general, a document sensor is installed on a sheet feed scanner so that the presence of any document in the sheet feeder can be detected. FIG. 1 is a front view showing a document sensing system in a conventional sheet feed scanner. As shown in FIG. 1, the document sensor 100 includes an optical sensor 110, a light emitter 120, a rocking lever 130 and a key peg 140. The optical sensor 110 and the light emitter 120 are attached to the sheet feeder (not shown) on each side of the rocking lever 130. The key peg 140 is also attached to the sheet feeder after passing through a hole in the rocking lever 130. Thus, the rocking lever 130 is free to rotate using the key peg 140 as a pivot. The light emitter 120 is positioned in such a way that a beam of light 122 from the light emitter 120 will go straight into the optical sensor 110 unimpeded.
Before a document (not shown) is fed into the sheet feeder, one end of the rocking lever 130 will cut across the path of the beam 122. Hence, the light beam 122 can never reach the optical sensor 110. Without receiving any light, the light sensor 110 will transmit a signal to a circuit chip (not shown) so that the chip jumps to a xe2x80x9cno documentxe2x80x9d logic state.
FIG. 2 is a side view of the document sensing system in FIG. 1. When a document 150 is fed in direction 152 into the sheet feeder, the document 150 pushes the rocking lever 130 and swings its upper end to one side so that the light beam 122 is able to project straight ahead to the optical sensor 110 unimpeded. On picking up the light beam 122, the optical sensor 110 transmits another signal to the circuit chip so that the chip switches to a xe2x80x9cdocument presentxe2x80x9d logic state.
As shown in FIGS. 1 and 2, the presence or absence of a document 150 in the sheet feeder depends on the light emitter 120/light sensor 110 system. The demand for a light emitter and a light sensor increases production cost of the optical scanner.
Accordingly, one object of the present invention is to provide a document sensor for a sheet feed scanner that does not require the incorporation of a light emitter and an optical sensor. Hence, overall production cost of the document sensing system is greatly reduced.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a document sensor for detecting the presence or absence of a document in a sheet feeder. The document sensor mounts on the sheet feeder. The document sensor at least includes a printed circuit board, a key peg and a rocking lever. The printed circuit board is attached to the sheet feeder. The printed circuit board contains a first lead wire and a second lead wire. The first lead wire and the second lead wire are separate from each other. The key peg passes through a hole in the rocking lever before attaching to the sheet feeder so that the rocking feeder may rotate using the key peg as a pivot. A conductive element is attached to the rocking lever so that the first lead wire and the second lead wire may be electrically connected together through a rotary motion of the rocking lever.
In one embodiment of this invention, the rocking lever has a linear shape and the conductive element is positioned at one end of the rocking lever. The conductive element may be an electroplated conductive layer on the rocking lever or a conductive plate attached to the rocking lever through rivets. Furthermore, the entire rocking lever may be made from a conductive material. One major design criteria of the rocking lever is the capacity to join up the first lead wire and the second lead wire selectively.
This invention also provides a method for sensing the presence or absence of a document inside a sheet feeder. The document sensing method includes the following steps. In step one, a document sensor is provided. The document sensor is attached to the sheet feeder. The document sensor comprises a first lead wire, a second lead wire and a driven element. The first lead wire and the second lead wire are detached from each other but are electrically connected together through the driven element. In step two, a document is fed into the sheet feeder. The entrance of a document pushes the driven element away from either the first lead wire or the second lead wire, breaking the electrical connection between the first and the second lead wire. Hence, the presence of a document in the sheet feeder can be detected. In step three, the document is pulled away from the sheet feeder. The driven element moves back to the original position and reforms the electrical connection between the first lead wire and the second lead wire. Hence, the absence of a document in the sheet feeder can be detected.
This invention also provides an alternative method for sensing the presence or absence of a document inside a sheet feeder. The document sensing method includes the following steps. In step one, a document sensor is provided. The document sensor is attached to the sheet feeder. The document sensor comprises a first lead wire, a second lead wire and a driven element. The driven element is detached at least from either the first lead wire or the second lead wire. In step two, a document is fed into the sheet feeder. The entrance of a document pushes the driven element to make an electrical connection between the first lead wire and the second lead wire. Hence, the presence of a document in the sheet feeder can be detected. In step three, the document is pulled away from the sheet feeder. The driven element moves back to the original position, breaking contact with at least either the first lead wire or the second lead wire again. Hence, the absence of a document in the sheet feeder can be detected.
In brief, by attaching a conductive element to the rocking lever or fabricating the rocking lever with conductive material, an electrical connection or disconnection between the first lead and the second lead wire can be selected through a rotation. Ultimately, internal logic states of a silicon chip can be controlled. The document sensing system has a simple structure and circuit design and hence the production cost is low.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.